Ci a ion: Topolᡠ, L.; Kocáb, D.;
H ubý, P.; Jakubka, L.; Hoduláko á,
M.; Halamo á, R. The E ec o
Specimen Size on Acous ic Emission
Pa ame e s and App oxima e
Posi ion o De ec s Ob ained du ing
Des uc i e Tes ing o Cemen i ious
and Alkali-Ac i a ed Deg aded
Fine-G ained Ma e ials. Ma e ials
2023,16, 3527. h ps://doi.o g/
10.3390/ma16093527
Academic Edi o s: Mikołaj
Mi´skiewicz and Danu a
Ba na -Hunek
Recei ed: 3 Ap il 2023
Re ised: 24 Ap il 2023
Accep ed: 2 May 2023
Published: 4 May 2023
Copy igh : © 2023 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
ma e ials
A icle
The E ec o Specimen Size on Acous ic Emission Pa ame e s
and App oxima e Posi ion o De ec s Ob ained du ing
Des uc i e Tes ing o Cemen i ious and Alkali-Ac i a ed
Deg aded Fine-G ained Ma e ials
Libo Topolᡠ1,* , Dalibo Kocáb1, Pe H ubý2, Luboš Jakubka 1, Michaela Hoduláko á1
and Romana Halamo á1
1Facul y o Ci il Enginee ing, B no Uni e si y o Technology, Ve eˇ í331/95, 60200 B no, Czech Republic;
dalibo .kocab@ u b .cz (D.K.); lubos.jakubka@ u b .cz (L.J.); [email p o ec ed].cz (M.H.);
omana.halamo a@ u b .cz (R.H.)
2Facul y o Chemis y, B no Uni e si y o Technology, Pu kyˇno a 464, 61200 B no, Czech Republic;
[email p o ec ed]
*Co espondence: libo . opola @ u b .cz; Tel.: +420-541-147-664
Abs ac :
Two sizes o es samples we e selec ed o in es iga e he e ec o size on he le el o
deg ada ion. The smalle es specimens had dimensions o 40
×
40
×
160 mm, and he la ge ones
had dimensions o 100
×
100
×
400 mm. Bo h sizes o es specimens we e always made o he
same mo a . In one case, Blas Fu nace Cemen was chosen as he binde . In he o he case, i was
an alkali-ac i a ed ma e ial as a possibly mo e en i onmen ally economical subs i u e. Bo h ypes
o ma e ial we e deposi ed in h ee deg ading solu ions: magnesium sulpha e, ammonium ni a e
and ace ic acid. The e e ence se was s o ed in a wa e ba h. A e six mon hs in he deg ada ion
solu ions, a s a ic elas ic modulus was de e mined o he specimens du ing his es , and he acous ic
emission was measu ed. Acous ic emission pa ame e s we e e alua ed: he numbe o hi s, he
ampli ude magni ude and a slope om he ampli ude magni ude e sus ime ( his slope should
co espond o he Kaise e ec ). Fo mos o he pa ame e s s udied, he size e ec was mo e e iden
o he mo e deg aded specimens, i.e., hose placed in agg essi e solu ions. The app oxima e loca ion
o eme ging de ec s was also de e mined using linea localisa ion o smalle specimens whe e he
deg ada ion e ec was mo e signi ican . In mo e agg essi e en i onmen s (ace ic acid, ammonium
ni a e), he highe esis ance o ma e ials based on alkaline-ac i a ed slag was mo e e iden , e en in
he case o la ge es bodies. The expe imen s show ha he acous ic emission esul s ag ee wi h he
esul s o he s a ic modulus o elas ici y.
Keywo ds:
size e ec ; deg ada ion; acous ic emission me hod; s a ic modulus o elas ici y; Kaise
e ec ; blas u nace slag; blas u nace cemen ; linea localisa ion
1. In oduc ion
Thanks o i s e sa ili y, a ailabili y, qui e su icien du abili y, ela i ely low p ice and
easy handling, conc e e has been and will con inue o be he mos common cons uc ion
ma e ial a ound he wo ld. Howe e , conc e e p oduc ion is associa ed wi h a la ge
consump ion o na u al esou ces and ene gy, as well as wi h signi ican CO
2
emissions,
pa icula ly due o he p esence o cemen as essen ial conc e e componen . I is es ima ed
ha up o one on o CO
2
is eleased du ing he p oduc ion o one on o Po land cemen [
1
],
and acco ding o S a is a, Inc. (Be lin, Ge many) [
2
] 4.4 billion me ic ons o cemen we e
p oduced in 2021. Gene ally, cemen p oduc ion co esponds o 5 o 8% o global CO
2
emissions [
3
]. The e o e, e o s o eplace cemen pa ially o ully by indus ial by-
p oduc s [
4
–
6
] and was e alumino-silica e sou ces such as slags and ly ashes ha e been
inc easing. Alongside o he al e na i e binde s such as calcium sul oalumina e cemen s o
Ma e ials 2023,16, 3527. h ps://doi.o g/10.3390/ma16093527 h ps://www.mdpi.com/jou nal/ma e ials
Ma e ials 2023,16, 3527 2 o 17
supe sul a ed cemen s [
7
], alkali-ac i a ed cemen less binde s ha e a ac ed inc easing
scien i ic a en ion du ing he las decades.
Mos building s uc u es a e subjec ed o comp essi e, ensile, momen loads and shea
loads du ing hei se ice li e—and o he ex e nal deg ading in luences. Fo example, huge
amoun s o conc e e based on o dina y Po land cemen ha e been used as cons uc ion
ma e ials o sewe s and was ewa e ea men plan s. Exposu e o an agg essi e, acid- ich
en i onmen leads o se e e deg ada ion [
8
,
9
]. Fo hese easons, i is necessa y o look
o ma e ials ha esis deg ada ion be e han ma e ials based on he o dina y Po land
cemen . Addi ionally, while cemen is s ill he mos commonly used binde , al e na i es in
he o m o alkali-ac i a ed ma e ials a e eme ging [10].
Alkali-ac i a ed ma e ials a e based on sui able aluminosilica e p ecu so s wi h a
su icien ly high con en o amo phous phase, such as g anula ed blas u nace slag, ly ash
and me akaolin. In sho , a e he dissolu ion o he amo phous phase, which is acili a ed
by he p esence o an alkaline ac i a o , usually sodium wa e glass o sodium hyd oxide
solu ion, polycondensa ion eac ions ake place and hyd a ion p oduc s wi h binding
p ope ies a e o med. The binde s uc u e and composi ion depend on he chemis y o
bo h aluminosilica e p ecu so s and ac i a o s, as well as on he cu ing condi ions and
o he pa ame e s. I can be summa ised ha he main hyd a ion p oduc o blas u nace
slag alkaline ac i a ion is calcium–aluminium–silica e–hyd a e, as a de i a e o he C-S-H
known om hyd a ion Po land cemen sys ems, while he alkaline ac i a ion o ly ash and
me akaolin o ms a mo e c oss-linked h ee-dimensional s uc u e o sodium–aluminium–
silica e–hyd a e [
11
]. To each su icien ly high ea ly age s eng h, me akaolin and ly
ash usually equi e a high amoun o ac i a o and hea cu ing, which means addi ional
economic and echnological demands. Tha is why alkali-ac i a ed ma e ials based on he
Blas Fu nace Slag, alkali-ac i a ed using he mix u e o sodium wa e glass and sodium
hyd oxide, we e used in his s udy.
Mos o he ecen s udies dealing wi h he chemical deg ada ion o cemen -based
ma e ial a e limi ed o one size o es specimens, e.g., [
12
–
16
]. E en s udies on he chemical
deg ada ion o alkali-ac i a ed ma e ials a e usually pe o med on small specimens o he
same size wi hin a gi en piece o esea ch, e.g., [
17
–
19
]. In ou case, we ocused on he
e ec o deg ada ion on di e en specimen sizes o wo mo a s on he base o CEM III/A
and alkali-ac i a ed ma e ial. Those ma e ials we e chosen due o hei simila indus ial
use and compa able p ope ies.
Size e ec is widely discussed o commonly used conc e es ( ein o ced o un ein-
o ced) [
20
,
21
] in e ms o ac u e mechanics [
22
,
23
] o heo e ical calcula ions o mod-
els [
24
,
25
]. In o he wo ks, o example [
26
], esea che s ha e es ed di e en sizes o
conc e e block specimens o comp essi e s eng h unde dynamic uniaxial loads.
Ve y ew s udies ha e e alua ed he e ec o sample size on deg aded specimens
using simul aneous non-des uc i e me hods. Howe e , in he case o labo a o y s udies
using small specimens (in ci il enginee ing, di e en ypes o pas es), esea che s can
make signi ican inaccu acies in hei conclusions. Using la ge specimens inc eases he
de ec isk, allowing he deg adan o pene a e mo e easily. Thus, usually, be e esul s
(i.e., comp essi e s eng h, e c.) a e ob ained hanks o he use o small specimens wi h
dimensions such as 20
×
20
×
100 mm. Ou esea ch also in ol es using he same mix u es
o small and la ge es specimens, which is no commonly ound in he li e a u e. This
way, he ad e se e ec s o using di e en ypes and amoun s o agg ega e in he mix u e
we e elimina ed.
Ano he aspec ha signi ican ly dis inguishes his pape om many o he s is he use
o he acous ic emission me hod o e eal he e ec o he size o he deg aded specimens
on he pa ame e s ob ained. The acous ic emission me hod was applied du ing he s a ic
modulus o elas ici y es . This pape , he e o e, looks a he e ec o he size o he es
specimens on he pa ame e s ob ained du ing des uc i e es ing.
Ma e ials 2023,16, 3527 3 o 17
2. Ma e ials
Alkali-ac i a ed blas u nace slag binde sys ems we e p epa ed using slag wi h a
Blaine ineness o 400 m
2·
kg
−1
(A celo Mi al Os a a, s. .o., Czech Republic). The slag’s
phase composi ion was de e mined by X- ay powde di ac ion (XRD) using he Rie eld
me hod wi h in e nal s anda d (CaF
2
). The amo phous con en o slag was abou 70.5%.
The main c ys alline phases we e ake mani e (19.8%), calci e (6.7%), qua z (2.7%), and
me wini e (0.4%). Liquid sodium wa e glass—silica e modulus (Ms) = 0.5 (VodníSklo, a.s.,
Czech Republic)—was used as an alkaline ac i a o in he 6% Na
2
O- ela ed dose pe he slag
weigh . The compa a i e cemen i ious binde was p epa ed using he
CEM III/A 32.5 R
(Ho néS nie cemen plan , Cemmac s. .o., Slo akia). The chemical composi ions o he
Blas Fu nace Slag and Blas Fu nace Cemen we e de e mined using X- ay luo escence
analysis (XRF), as shown in Table 1.
Table 1.
Chemical composi ions (%) o Blas Fu nace Slag (BFS) and Blas Fu nace Cemen
(BFC = CEM III/A) as de e mined by X- ay luo escence.
CaO SiO2MgO Al2O3SO3TiO2K2O MnO Na2O Fe2O3LOI
BFS 37.0 39.4 8.6 8.1 1.4 0.3 1.2 0.9 0.4 0.7 2
BFC 45.6 31.6 5.8 7.4 3.3 0.4 0.8 0.6 0.3 1.4 2.8
P epa a ion and Composi ion o Tes ing Specimens—Mo a s
The es ing specimens we e p epa ed as p esc ibed in he Eu opean s anda d EN 196-1;
he composi ion o each mix u e is in Table 2. The mixing ook 3 min, and he ac i a o
and he slag (o CEM III/A) we e mixed using a low speed du ing he ini ial 30 s, and
hen he s anda dised sand was added and mixed o ano he 30 s. This was ollowed by
high-speed mixing o 30 s and con inued by wiping he walls o he con aine o 30 s. A
inal mixing using high speed o 60 s was implemen ed a he end. The labo a o y mixe
(Ki chenAid Robo A isan 175) was used o he mo a p epa a ion. The p epa ed mix u e
was cas in o he moulds and compac ed on he compac ing able o 30 s o elimina e he
ai en apped. The es ing specimens we e demoulded a e 24 h and pu in o wa e s o age,
whe e hey we e s o ed o 28 days a 25
◦
C ( he specimens we e no s o ed in a empe ed
oom; he empe a u e o 25
◦
C was he long- e m a e age o he pe iod unde s udy).
Then, he deg ada ion es ing s a ed wi h he imme sion o he es ing specimens in he
speci ic solu ions (magnesium sulpha e (50 g/L), ammonium ni a e (6 mol/dm
3
) and
ace ic acid (pH = 3), ap wa e as a e e ence). The sand- o-binde mass a io in mo a s was
3:1. The wa e - o-binde a io (w/b) was he same (0.45) o bo h es ed binde s. Cemen
(CEM III/A 32.5R) was chosen as he binde because i was blas - u naced acco ding o
he ma king and had minimum admix u es. Blas - u nace slag is he mos commonly used
cemen eplacemen in he Czech Republic’s cemen - ee mixes.
Table 2. Composi ion o indi idual mo a mixes (weigh in g ams).
Ma e ial Blas Fu nace Slag CEM III/A Sand Sodium Wa e
Glass (Ms = 0.5) Wa e
AAS mo a * 22.0 – 66.1 4.6 7.2
CEM mo a ** – 22.5 67.4 – 10.1
* AAS mo a is made based on alkali-ac i a ed blas u nace slag (AAS) binde . ** CEM mo a is made based on
blas u nace cemen (CEM) binde .
3. Tes ing Me hods
3.1. Desc ip ion o Deg ada ion En i onmen s
Deg ada ion en i onmen s we e designed o simula e a ious deg ada ion mecha-
nisms and p o ide e e ence specimens as a blank. Wa e embedding o specimens was
chosen as a e e ence. A solu ion o ace ic acid o pH
≈
3 was selec ed o simula e be-
ha iou unde he acidic condi ions, hus he decalci ica ion mechanism along wi h he
Ma e ials 2023,16, 3527 4 o 17
pa ial dissolu ion o he silicon-con aining gels. Nex , decalci ica ion wi hou he aligned
dissolu ion o silica e uni s was s udied using he 6 mol/dm
3
ammonium ni a e solu ion.
Sulpha e co osion was hen simula ed using he 50 g/L solu ions o magnesium sulpha e.
Deg ada ion solu ions we e ully eplaced e e y 28 days o s imula e he deg ada ion
p ocess. The pH o he ace ic acid en i onmen was measu ed and kep a he alue o
app oxima ely pH ≈3 by adding an ex a dose o ace ic acid h ee imes pe week.
The ongoing p ocesses we e obse ed by measu ing he pH (Me le Toledo Se en-
Compac
™
Duo S213 using an InLab Rou ine elec ode wi h ange o pH 0–14) o all he
solu ions be o e eplacemen wi h esh ones. The p og ess in ime can be seen in Table 3.
I can be seen om he able ha e en hough one day he pH was educed o a alue close
o 3 ( o ace ic acid), jus be o e he exchange he alue was highe again.
Table 3. pH alue o solu ions measu ed jus be o e exchange o esh solu ions.
Wa e Ace ic Acid Magnesium Sulpha e Ammonium Ni a e
Days AAS CEM AAS CEM AAS CEM AAS CEM
0 7.45 3 8.1 6.24
28 12.48 10.78 4.99 5.1 9.25 9.67 9.37 9.64
56 12.65 10.57 5.37 5.49 9.39 9.53 9.57 9.71
84 9.45 7.73 4.52 4.92 8.89 9.47 9.02 9.71
112 9.66 8.53 4.57 4.89 8.87 9.3 9.11 9.13
140 9.03 8.33 4.5 4.64 8.9 9.06 8.69 8.13
168 8.35 8.05 4.24 4.17 8.58 8.91 8.58 8.66
Each binde ype’s specimens (3 pcs o 100
×
100
×
400 mm and 21 pcs o
40
×
40
×
160 mm) we e placed in o one con aine o a speci ic solu ion (
app ox. 50 L
).
The olume a io be ween he specimens and he deg ada ion solu ion was 1:3 du ing he
es ing pe iod. Con aine s we e kep a labo a o y condi ions (20
◦
C) o he whole es ing
pe iod. The e ec o deg ada ion media was in ensi ied using he ai s eam bubbling.
3.2. S a ic Modulus o Elas ici y and Comp essi e S eng h
A e emo ing he es specimens om he indi idual deg ada ion solu ions, he
s a ic modulus o elas ici y and hen he p isma ic comp essi e s eng h we e de e mined
o all specimens. The modulus o elas ici y es was pe o med acco ding o ISO 1920-10.
The loading p og ess o he es specimens is shown in Figu e 1. The basic load s ess was
always 0.5 MPa ( he applied o ce was 1 kN o smalle specimens and 5 kN o bigge
specimens), and he uppe load s ess was 1/3 o he expec ed comp essi e s eng h. The
comp essi e s eng h was es ima ed based on he esul s o pa allel es s pe o med on o he
specimens. S ill, hese es s a e no desc ibed in his pape ( hese we e he lexu al ensile
s eng h, he comp essi e s eng h on agmen s and he dynamic modulus o elas ici y).
The loading o smalle specimens was ca ied ou in he DELTA 3-600 (FORM+TEST) es
p ess and he loading o bigge specimens in he ALPHA 3-3000S (FORM+TEST) es p ess,
in bo h cases using he P o eus so wa e. The de o ma ions o he es specimens we e
measu ed du ing es ing using wo elec onic s ain ansduce s LD-DD1-2 (FORM+TEST).
Using he Spide 8 da a logge (HBM), a eco d o he applied o ce and de o ma ion o
he es specimens was ob ained h oughou he es . A e he modulus o elas ici y es ,
comp essi e s eng h was de e mined on all es specimens acco ding o EN 12390-3.
Ma e ials 2023,16, 3527 5 o 17
Ma e ials 2023, 16, x FOR PEER REVIEW 5 o 18
Figu e 1. The loading p og ess o he es specimens.
3.3. Acous ic Emission Me hod
An acous ic emission me hod is a ool o he non-des uc i e moni o ing o ac i e
dynamic changes in a s essed ma e ial [27]. The basis o his me hod is he con inuous
moni o ing o he acous ic esponse caused by he ini ia ion and p opaga ion o damage
unde s ess (mechanical, chemical o he mal) [28–30]. A ansien elas ic wa e is
gene a ed locally due o he apid elease o ene gy as he s essed ma e ial p opaga es
h ough he ma e ial un il i eaches he su ace. The su ace wa es a e hen cap u ed by
piezoelec ic senso s and subsequen ly con e ed o elec ical signals [31]. The elec ical
signals a e ampli ied, p ocessed and inally s o ed in a eco ding de ice. Unlike o he non-
des uc i e de ec ion me hods, acous ic emission signals can only be de ec ed when
damage occu s wi hin he ma e ial [32].
Commonly used acous ic emission signal cha ac e is ics a e shown in hi o m in
Figu e 2, including ampli ude, ene gy, numbe o ings, ise ime and du a ion. The
acous ic emission ampli ude co esponds o he poin o maximum alue, exp essed on a
decibel scale. The ene gy o he wa e o m is he a ea abo e he h eshold and below he
en elope cu e. Any oscilla ion o he elec ical signal exceeding a h eshold alue is
conside ed a ing coun . The ing coun can e lec he signal s eng h and equency and
is widely used o e alua e acous ic emission ac i i ies. The ene gy and ampli ude o
acous ic emission can be used o cha ac e ise he magni ude o damage [33,34]. The ime
be ween he s a ime o a single acous ic emission signal and he peak ampli ude is called
he ise ime, and he ime be ween he s a ime o a single acous ic emission signal and
he decay ime is called he du a ion [35]. In his s udy, only wo o he abo e pa ame e s
we e used: he numbe o eco ded hi s and he AE ampli ude.
Figu e 1. The loading p og ess o he es specimens.
3.3. Acous ic Emission Me hod
An acous ic emission me hod is a ool o he non-des uc i e moni o ing o ac i e
dynamic changes in a s essed ma e ial [
27
]. The basis o his me hod is he con inuous
moni o ing o he acous ic esponse caused by he ini ia ion and p opaga ion o damage
unde s ess (mechanical, chemical o he mal) [
28
–
30
]. A ansien elas ic wa e is gene a ed
locally due o he apid elease o ene gy as he s essed ma e ial p opaga es h ough he
ma e ial un il i eaches he su ace. The su ace wa es a e hen cap u ed by piezoelec ic
senso s and subsequen ly con e ed o elec ical signals [
31
]. The elec ical signals a e
ampli ied, p ocessed and inally s o ed in a eco ding de ice. Unlike o he non-des uc i e
de ec ion me hods, acous ic emission signals can only be de ec ed when damage occu s
wi hin he ma e ial [32].
Commonly used acous ic emission signal cha ac e is ics a e shown in hi o m in
Figu e 2, including ampli ude, ene gy, numbe o ings, ise ime and du a ion. The
acous ic emission ampli ude co esponds o he poin o maximum alue, exp essed on
a decibel scale. The ene gy o he wa e o m is he a ea abo e he h eshold and below
he en elope cu e. Any oscilla ion o he elec ical signal exceeding a h eshold alue is
conside ed a ing coun . The ing coun can e lec he signal s eng h and equency and is
widely used o e alua e acous ic emission ac i i ies. The ene gy and ampli ude o acous ic
emission can be used o cha ac e ise he magni ude o damage [
33
,
34
]. The ime be ween
he s a ime o a single acous ic emission signal and he peak ampli ude is called he ise
ime, and he ime be ween he s a ime o a single acous ic emission signal and he decay
ime is called he du a ion [
35
]. In his s udy, only wo o he abo e pa ame e s we e used:
he numbe o eco ded hi s and he AE ampli ude.
The Kaise e ec p inciple appea ed du ing he specimens’ cyclic loading (see
Figu e 3
).
The AE signals we e insigni ican unless he s ess exceeded he p e iously applied max-
imum p essu e. F om poin A o B, he AE signals we e eleased con inuously, bu a e
unloading up o poin C and eloading un il poin B, no signal could be obse ed unless
i exceeded poin B. This phenomenon is called i e e sibili y and is known as he Kaise
e ec . As long as he loading con inued, he AE signals we e emi ed. When he loading
cycles eached highe s ess in poin D, he ma e ial en e ed an uns able phase in which
he p e ious mic oc acks expanded signi ican ly and se ious damage occu ed. AE signals
could be seen e en be o e eaching poin D, which means ha he Kaise e ec a he highe
s ess le el ends o dec ease [37,38].

Ma e ials 2023,16, 3527 6 o 17
Ma e ials 2023, 16, x FOR PEER REVIEW 6 o 18
Figu e 2. Schema ic diag am o AE pa ame e s [36].
The Kaise e ec p inciple appea ed du ing he specimens’ cyclic loading (see Figu e
3). The AE signals we e insigni ican unless he s ess exceeded he p e iously applied
maximum p essu e. F om poin A o B, he AE signals we e eleased con inuously, bu
a e unloading up o poin C and eloading un il poin B, no signal could be obse ed
unless i exceeded poin B. This phenomenon is called i e e sibili y and is known as he
Kaise e ec . As long as he loading con inued, he AE signals we e emi ed. When he
loading cycles eached highe s ess in poin D, he ma e ial en e ed an uns able phase in
which he p e ious mic oc acks expanded signi ican ly and se ious damage occu ed. AE
signals could be seen e en be o e eaching poin D, which means ha he Kaise e ec a
he highe s ess le el ends o dec ease [37,38].
Figu e 3. P inciple o Kaise e ec .
Linea (one-dimensional) localisa ion o acous ic sou ces was pe o med conside ing
he wa e p opaga ion eloci y o each ma e ial ype sepa a ely (de e mined om
ul asonic wa es); see Figu e 4. Localised AE e en s we e eco ded along he line be ween
he ansduce s and used o subsequen AE analysis o exclude any o he ecei ed signals
[39].
Figu e 2. Schema ic diag am o AE pa ame e s [36].
Ma e ials 2023, 16, x FOR PEER REVIEW 6 o 18
Figu e 2. Schema ic diag am o AE pa ame e s [36].
The Kaise e ec p inciple appea ed du ing he specimens’ cyclic loading (see Figu e
3). The AE signals we e insigni ican unless he s ess exceeded he p e iously applied
maximum p essu e. F om poin A o B, he AE signals we e eleased con inuously, bu
a e unloading up o poin C and eloading un il poin B, no signal could be obse ed
unless i exceeded poin B. This phenomenon is called i e e sibili y and is known as he
Kaise e ec . As long as he loading con inued, he AE signals we e emi ed. When he
loading cycles eached highe s ess in poin D, he ma e ial en e ed an uns able phase in
which he p e ious mic oc acks expanded signi ican ly and se ious damage occu ed. AE
signals could be seen e en be o e eaching poin D, which means ha he Kaise e ec a
he highe s ess le el ends o dec ease [37,38].
Figu e 3. P inciple o Kaise e ec .
Linea (one-dimensional) localisa ion o acous ic sou ces was pe o med conside ing
he wa e p opaga ion eloci y o each ma e ial ype sepa a ely (de e mined om
ul asonic wa es); see Figu e 4. Localised AE e en s we e eco ded along he line be ween
he ansduce s and used o subsequen AE analysis o exclude any o he ecei ed signals
[39].
Figu e 3. P inciple o Kaise e ec .
Linea (one-dimensional) localisa ion o acous ic sou ces was pe o med conside ing
he wa e p opaga ion eloci y o each ma e ial ype sepa a ely (de e mined om ul a-
sonic wa es); see Figu e 4. Localised AE e en s we e eco ded along he line be ween he
ansduce s and used o subsequen AE analysis o exclude any o he ecei ed signals [
39
].
Ma e ials 2023, 16, x FOR PEER REVIEW 7 o 18
Figu e 4. Schema ic diag am o AE linea localisa ion.
In he expe imen s p esen ed he e, he moni o ing o AE ac i i y was pe o med wi h
a dual-channel uni DAKEL ZEDO (ZD Rpe y, P ague, Czech Republic) wi h he
ollowing inpu pa ame e s o hi -de ec o :
• The h eshold alue o indi idual AE hi s was se a 200% abo e he noise le el;
• A sampling o AE hi s was se o 5 MHz;
• The cu -o equency o he low-pass il e was se o 500 kHz.
The o al gain was 34 dB, bu only by p e-ampli ie . The AE senso s we e a ached o
he specimens wi h beeswax in a hin laye ; see Figu e 5. The loca ion o he acous ic
emission senso s on he specimen was p opo ional o he size o he es specimen.
Figu e 5. Loca ion o acous ic emission senso s on a smalle (le ) and bigge ( igh ) specimen.
4. The Ongoing Chemical P ocesses
The deg ada ion o bo h es ed binde sys ems due o he imme sion in ammonium
ni a e and ace ic acid was ela ed o decalci ica ion. Decalci ica ion ep esen s a p ocess
whe e he simul aneous leaching o Ca2+ om he binde gel con empo aneously wi h he
o ma ion o co esponding calcium sal s occu s. This is ela ed o he simul aneous
educ ion o he C/S a io in he binde gel, which can esul in he esidual S-H gel wi h
Figu e 4. Schema ic diag am o AE linea localisa ion.
Ma e ials 2023,16, 3527 7 o 17
In he expe imen s p esen ed he e, he moni o ing o AE ac i i y was pe o med wi h
a dual-channel uni DAKEL ZEDO (ZD Rpe y, P ague, Czech Republic) wi h he ollowing
inpu pa ame e s o hi -de ec o :
•The h eshold alue o indi idual AE hi s was se a 200% abo e he noise le el;
•A sampling o AE hi s was se o 5 MHz;
•The cu -o equency o he low-pass il e was se o 500 kHz.
The o al gain was 34 dB, bu only by p e-ampli ie . The AE senso s we e a ached
o he specimens wi h beeswax in a hin laye ; see Figu e 5. The loca ion o he acous ic
emission senso s on he specimen was p opo ional o he size o he es specimen.
Ma e ials 2023, 16, x FOR PEER REVIEW 7 o 18
Figu e 4. Schema ic diag am o AE linea localisa ion.
In he expe imen s p esen ed he e, he moni o ing o AE ac i i y was pe o med wi h
a dual-channel uni DAKEL ZEDO (ZD Rpe y, P ague, Czech Republic) wi h he
ollowing inpu pa ame e s o hi -de ec o :
• The h eshold alue o indi idual AE hi s was se a 200% abo e he noise le el;
• A sampling o AE hi s was se o 5 MHz;
• The cu -o equency o he low-pass il e was se o 500 kHz.
The o al gain was 34 dB, bu only by p e-ampli ie . The AE senso s we e a ached o
he specimens wi h beeswax in a hin laye ; see Figu e 5. The loca ion o he acous ic
emission senso s on he specimen was p opo ional o he size o he es specimen.
Figu e 5. Loca ion o acous ic emission senso s on a smalle (le ) and bigge ( igh ) specimen.
4. The Ongoing Chemical P ocesses
The deg ada ion o bo h es ed binde sys ems due o he imme sion in ammonium
ni a e and ace ic acid was ela ed o decalci ica ion. Decalci ica ion ep esen s a p ocess
whe e he simul aneous leaching o Ca2+ om he binde gel con empo aneously wi h he
o ma ion o co esponding calcium sal s occu s. This is ela ed o he simul aneous
educ ion o he C/S a io in he binde gel, which can esul in he esidual S-H gel wi h
Figu e 5. Loca ion o acous ic emission senso s on a smalle (le ) and bigge ( igh ) specimen.
4. The Ongoing Chemical P ocesses
The deg ada ion o bo h es ed binde sys ems due o he imme sion in ammonium
ni a e and ace ic acid was ela ed o decalci ica ion. Decalci ica ion ep esen s a p ocess
whe e he simul aneous leaching o Ca
2+
om he binde gel con empo aneously wi h
he o ma ion o co esponding calcium sal s occu s. This is ela ed o he simul aneous
educ ion o he C/S a io in he binde gel, which can esul in he esidual S-H gel wi h
limi ed u ili y alue ins ead o he C-S-H o he C-A-S-H. The alkali-ac i a ed blas u nace
slag has highe esis ance agains decalci ica ion compa ed o O dina y Po land Cemen ,
as s a ed in s udies such as [
40
–
42
]. The alkali-ac i a ed blas u nace slag binde gel
has mo e in ensely c oss-linked silica e chains, since alumina uni s a e implemen ed in
he binde gel s uc u e (C-A-S-H) compa ed o he main hyd a ion p oduc o cemen
hyd a ion (C-S-H gel). Mo eo e , he A-S-H can o m a s able passi a ion laye . Nex , he
pH o he po e solu ion o he alkali-ac i a ed slag is highe han he one in cemen i ious
sys ems. Decalci ica ion due o he e ec o he ammonium ni a e akes place only when
he pH o he solu ion is lowe han 9.25 [
43
], so since he ini ial pH o he alkali-ac i a ed
sys em was highe , i helped o p e en deg ada ion.
Ma e ials 2023,16, 3527 8 o 17
Finally, he e was no po landi e in alkali-ac i a ed slag. Po landi e p esen in a
hyd a ed cemen i ious sys em can be easily leached ou om he ma ix. This p o ec s
he C-S-H gel om decalci ica ion, bu simul aneously, once he po landi e is leached,
he po es o he ma ix a e opened and he a e o deg ada ion is inc eased, since he
pe meabili y o he ma ix inc eases.
The bigge he specimen, he lowe de e io a ion o p ope ies was obse ed. This can
be explained ia he mass a io be ween he deg ada ion medium and he specimen size.
Bigge specimens con ain mo e Ca
2+
in p opo ion o ele an anions in he deg ada ion
solu ion; hus, deg ada ion does no each such a a e ( olume and mass a io be ween he
specimen/liquid di e s o bigge and smalle specimens). Then, agg essi e solu ions do
no pene a e o such a dep h, and he esidual e ec i e non-a ec ed c oss-sec ion o he
specimen is mo e signi ican . This e ec was mo e se e e o he cemen i ious sys em.
No deg ada ion e ec o imme sion on he ap wa e was obse ed, ega dless o
he specimen size and he ype o he binde . The imme sion in he 50 g/L solu ion o
magnesium sulpha e did no esul in any signi ican changes in he p ope ies o he
cemen i ious binde , no ma e he size o he specimen.
The deg ada ion o he calcium–silica e-based binde s due o he e ec o magnesium
sulpha e solu ion can be explained by he o ma ion o he expansi e p oduc as a p oduc
o he eac ion be ween he calcium ions in he ma ix and sulphu anions o he pene a ing
solu ion. These eac ion p oduc s can be gypsum, e ingi e and b uci e. The decalci ica ion
can be obse ed along wi h hose p ocesses, lea ing he pa ially decalci ied binde gel
behind [44].
The small es ing specimens p epa ed om alkali-ac i a ed slag mo a showed wo se
esis ance agains sulpha e co osion compa ed o he cemen i ious one. The e is a dis-
c epancy in he s udies compa ing deg ada ion esis ance be ween o dina y cemen and
alkali-ac i a ed slag.
Bel ame e al. and Mi hun e al. s a e a lowe esis ance o alkali-ac i a ed binde s
compa ed o cemen i ious ones; on he o he hand, o he s such as Allah edi e al. and
Bakha e e al. p esen ed a highe esis ance. The la ge specimens o alkali-ac i a ed
mo a did no show such apid de e io a ion o es ed p ope ies as he smalle ones. This
could, again, be ela ed o he a ec ed a ea o he specimen and he o e all a io be ween
he specimen and he agg essi e media [44–47].
5. Resul s and Discussion
5.1. Size E ec
The g aphs in Figu e 6show wo ep esen a i e s ess load cu es o de e mining he
s a ic modulus o elas ici y ( ed cu e). The plo s also show he hi eco d o he acous ic
emission in he o m o ampli ude (blue poin s). These poin s a e in e laced wi h a line
(linea eg ession) whose slope de e mines he in luence o he Kaise e ec [
48
–
50
] on
he acous ic emission signals. The highe slope o his line e lec s he mo e signi ican
demons a ion o he Kaise e ec . In he ma e ial ha exhibi s an ini ial ailu e unde a
speci ic load, he Kaise e ec desc ibes he absence o acous ic emission un il ha load
is exceeded. The Kaise e ec esul s om discon inui ies c ea ed in he ma e ial du ing
p e ious s eps ha do no mo e, expand, o p opaga e un il he o me s ess is exceeded.
The g aphs a e jus a demons a ion o he wo selec ed specimens. In he o he pa s
o he esul s, he indi idual se s will be ep esen ed by he a e ages o he alues and he
coe icien o a ia ion, see Tables 4and 5.
Ma e ials 2023,16, 3527 9 o 17
Ma e ials 2023, 16, x FOR PEER REVIEW 9 o 18
exceeded. The Kaise e ec esul s om discon inui ies c ea ed in he ma e ial du ing
p e ious s eps ha do no mo e, expand, o p opaga e un il he o me s ess is exceeded.
Figu e 6. Example o he loading specimens du ing s a ic modulus o elas ici y wi h he eco ding
o acous ic emission (ampli ude o hi s) o a smalle ( op g aph) and a bigge (bo om g aph)
specimen made o CEM III/A imme sed in he ace ic acid solu ion.
The g aphs a e jus a demons a ion o he wo selec ed specimens. In he o he pa s
o he esul s, he indi idual se s will be ep esen ed by he a e ages o he alues and he
coe icien o a ia ion, see Tables 4 and 5.
Figu e 6.
Example o he loading specimens du ing s a ic modulus o elas ici y wi h he eco ding o
acous ic emission (ampli ude o hi s) o a smalle (
op g aph
) and a bigge (
bo om g aph
) specimen
made o CEM III/A imme sed in he ace ic acid solu ion.
Table 4.
Tes esul s o CEM III/A-based mo a ( alues a e he a e age o h ee specimens wi h
coe icien o a ia ion).
Specimen Ec(GPa) c,p ism (Mpa) Numbe o Hi s (-) A e age AE
Ampli ude (dB) Slope (dB/s)
Smalle
Wa e 40.56 (0.009) 61.85 (0.103) 1443 (0.010) 41.9 (0.153) −0.027 (0.295)
Magnesium sulpha e 39.68 (0.010) 65.15 (0.069) 1213 (0.113) 46.8 (0.044) −0.037 (0.104)
Ammonium ni a e 9.44 (0.081) 10.78 (0.112) 262 (0.257) 39.4 (0.047) −0.012 (0.212)
Ace ic acid 18.17 (0.052) 12.37 (0.185) 263 (0.250) 36.4 (0.074) −0.005 (0.163)
Bigge
Wa e 40.99 (0.010) 66.55 (0.037) 318 (0.204) 46.1 (0.024) −0.030 (0.157)
Magnesium sulpha e 40.40 (0.010) 64.89 (0.017) 310 (0.299) 47.4 (0.019) −0.036 (0.078)
Ammonium ni a e 25.26 (0.024) 37.21 (0.126) 157 (0.441) 44.9 (0.056) −0.028 (0.374)
Ace ic acid 30.54 (0.014) 39.96 (0.017) 291 (0.231) 49.1 (0.106) −0.031 (0.158)
Ma e ials 2023,16, 3527 16 o 17
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Disclaime /Publishe ’s No e:
The s a emen s, opinions and da a con ained in all publica ions a e solely hose o he indi idual
au ho (s) and con ibu o (s) and no o MDPI and/o he edi o (s). MDPI and/o he edi o (s) disclaim esponsibili y o any inju y o
people o p ope y esul ing om any ideas, me hods, ins uc ions o p oduc s e e ed o in he con en .